It seems like it's based on computer models, so it really depends on how well the models predict reality. Just fitting past data will not be sufficient.
any serious modelling will involve predictive runs with a starting point in the past, then matching the output to available actual time series data up to present time. I would be very surprised if this scientists' models were not subjected to this kind of routine testing.
That's not sufficient. If you write 10 different models, each with 10s of thousands of parameters until you get the results you want, it doesn't matter how accurately the model seems to predict in the past. Modelling is a tricky business that easily falls prey to such "data snooping" methods.